The present invention relates to a control system, in particular a system for use with machinery having moving parts, such as press brakes, to detect objects in the path of the moving part and control the movement of the part accordingly.
A typical break press has a long anvil with a V-shaped groove along the top and a blade with a forward edge that fits into the groove of the anvil. To bend a piece of sheet metal, most machines drive a back-gauge into a position to align the material. The material is placed onto the anvil and may be slotted into guides provided by back-gauge clamps. The operator then activates the press, driving the blade down so that it comes into contact with, and then bends the sheet metal that has been placed over the groove of the anvil.
The controller (the device that controls movement of the blade) may be activated by mechanical means or by a presence sensing device. Mechanical means may be, for example, footswitches, double handed approach switches or the like. Presence sensing devices such as light curtains are placed in front of the blade and allow the blade to be activated by the operator removing hands from the sensing zone.
After a bend, the material can be difficult to remove from the anvil if the blade has not been set to retract far enough away from the work. For this reason, a press brake blade is often configured to retract to a height where the bent material can easily be removed, and a new piece placed onto the anvil. Opening the blade to a set height in this fashion reduces productivity and increases the workload of the operator as the operator must wait for the blade to first retract and then approach the next piece of material that is placed onto the anvil in response to activation of an approach switch.
This relatively large opening increases danger to the operator as there is a gap into which the operator may insert fingers or hands. Techniques such as having a programmable blade opening height for each stage of the bending process and/or a fast approach speed to the material have been used to improve productivity.
A number of systems have been devised to detect the presence of hands or fingers under the blade and to therefore avoid the possibility of crush injuries or entrapment.
For example, a system using laser beams projected along the underside of a blade may be used for this purpose and to improve productivity by permitting the blade to travel straight through the mute point in relative safety. An improved method has also been described in the applicant's own earlier patent application, published under International Publication Number WO03/104711. This invention discloses a device that is suitable for safety in that it may slow and stop the blade in response to a detected unsafe action. Other than stopping or slowing movement, it does not control movement of the blade in response to images received nor does it permit blade movement again until the operator re-activates the approach switch. Also, laser systems projected along the underside of the blade are known to suffer from vibration of the laser beam due to the length of the blade and are known to require periodic manual re-alignment.
To improve safety, the blade may be stopped a preset distance (often called the mute or pinch point) above the material and the approach switch required to be released and re-asserted again before the bending action restarts. This action reduces productivity as extra time is spent, during the process of aligning the material, activating the approach switch, waiting for the blade to approach the material and the releasing and reasserting of the approach switch at the mute point. Alternatively, as described in WO03/104711 and other patents, the zone in front of the blade is examined and the blade conditionally permitted to travel through the mute point without stopping, however, this method only operates if the area in front of the blade is shown to be safe, also operator control and perceived safety is reduced as the blade travels a relatively large distance before the blade comes into contact with the material. Also in this situation, the blade is not stopped just above the material, so the operator is not able to use the blade to ensure the material is positioned correctly.
Some modern press brake machines have associated computer systems that permit the material bend operations to be demonstrated graphically on a computer screen. A computer may also open the blade to an appropriate height for the bend that is being performed. However, if the material is oriented incorrectly when placed onto the anvil then either the wrong bend may be performed, or the operator may need to stop the machine and re-orient the material.
A further problem with existing press brakes arises when bending a box. During this operation, an operator may bend the two sides of the box then rotate the work piece 90 degrees to bend the back of the box. If the material isn't aligned correctly or if the material is not sitting flat on the anvil, then the left or right edge of the blade could be damaged, or the material crumpled due to the blade coming into contact with one of the up-stands. This would be likely to occur if the material is not aligned correctly when the approach switch is activated.
In order to avoid this problem, it is known to use a laser system to make the blade stop just above the up-stands or configure such a stop into the machine, thereby permitting the operator to ensure the material is positioned correctly for the blade to pass between the sides without coming into contact with them. Alternatively, the operator may lower the opening height of the blade to less than the height of the material upstands, potentially resulting in increased difficulty inserting and removing the bent material. Such systems however will result in decreased productivity due to the additional time added to the process.
Multiple devices may be required to achieve the various tasks mentioned above and this can result in increase system complexity, with the system having more parts to be damaged, calibrated connected to the machine, aligned, to fail during operation or to get in the way of the material, blade, anvil or the bending operation.
The present invention attempts to overcome at least in part some of the aforementioned problems.